The T. Rowe Price New Horizons Fund looks for small dynamic firms, and the occasional not-yet public start-up, that can grow much bigger.

Though Morningstar puts the $9.7 billion fund in the small-cap growth box, roughly 50% of its holdings have market values above $2.7 billion.

Founded more than 50 years ago, the New Horizons Fund (ticker: PRNXH) looks for small, dynamic companies that can grow over time into larger companies. Manager Henry Ellenbogen only buys small-cap stocks – searching...